Going with the flow

As I mentioned in my last post, invasive aquatic plants are a big concern- although we are still learning about how they impact invaded ecosystems (and it’s not necessarily bad), we do know that plants such as water hyacinth, Spartina spp., and milfoil can clog waterways, change habitat, and alter faunal communities. And, as we become more aware of the influence of climate change, there are worries that invasive aquatics are just getting started.

How does climate change play into this? I learned during my research this week that it does, in part, depend on which species we are talking about. There is some agreement that climate change will probably facilitate access to new places (Hellmann et al. 2008; Rahel & Olden 2008). As Arctic ice retreats, ships will be able to use routes north of Canada and Alaska for greater portions of the year, and current routes around the world may shift if populations and resource needs change due to an altered environment. Another concern is that, as temperatures in northern lakes moderate, there may be more pressure to manage the fish populations for sport fishing (which can introduce exotic species) and increase recreational boater access to these sites (with all the hitchhikers from other water bodies that entails). Warming waters could also increase the amount of suitable habitat invasive species encounter- the growth of Caulerpa spp., for example, is related to water temperature (Occhipinti-Ambrogi 2007), so we could see successful invasions spreading out toward the poles as the world’s oceans heat up. It is also likely that, as we deal with our own concerns about climate change, we will help invasives move into new locations. Water scarcity may become an issue in new locations as precipitation patterns change, leading to the construction of more reservoirs- reservoirs both provide new locations for recreational activity which can lead to species introductions and create bodies of still water which can be more susceptible to domination by certain invasive species (Rahel & Olden 2008). So are we looking at continued worldwide conquest? Well, that’s a hard one to answer. A study in Australia that modeled the future spread of lippia weed (Phyla canescens) in riparian areas found that, although rising temperatures would hypothetically open new areas for colonization, changes in rain fall would make certain areas less suitable because there wouldn’t be enough water (Murray et al. 2012). And changes in ocean salinity (both higher in some locations and lower in others) have a role to play- when looking at the spread of Spartina alterniflora in northern China, He et al. (2012) determined that salinity levels had greater importance than competition from other plants in success or failure to invade a habitat.

Photo from: Robert H. Mohlenbrock. USDA SCS. 1991. Southern wetland flora: Field office guide to plant species. South National Technical Center, Fort Worth. Courtesy of USDA NRCS Wetland Science Institute.

(In case you were wondering what alligatorweed looks like.)  Photo from: Robert H. Mohlenbrock. USDA SCS. 1991. Southern wetland flora: Field office guide to plant species. South National Technical Center, Fort Worth. Courtesy of USDA NRCS Wetland Science Institute.

However, there are also worries that invasives might actually help each other become dominant. A study in Connecticut found that invasive phragmites reeds actually helped native bullfrog larvae grow bigger and survive the larval stage better (Rogalski & Skelly 2012) which seems like a great thing, except that these same bullfrogs are invasive in the western US and phragmites there might help the frogs become completely dominant (when this type of synergy feeds and feeds upon itself, they call it ‘invasion meltdown’- what a bright future…). And water hyacinth, although having lower establishment, has higher growth in the presence of alligatorweed (Wundrow et al. 2012).

Do we have options for dealing with these invasives? Yes, although it will likely require sustained effort from everyone. Once again, effective management or eradication plans are species-dependent. Water lettuce is not cold hardy, so, in areas with ice cover in winter, manual removal can work to control it (of course, if global warming changes those winter patterns, we’ll need a new strategy) (Hellmann et al. 2008). Since hydrilla tubers can remain viable in soil for at least 4 years, it’s important to not only remove the plants that are there but also clear out the tubers (Doyle & Smart 2001)- this can be partially accomplished by drawing down the water level to encourage tuber sprouting and then exposing the tubers to desiccation, but you need to repeat the cycle multiple times plus use other removal techniques if you want to eradicate them. Treatment of phragmites along the coast of Cape Cod involved yearly herbicide starting in 2002 (Lombard et al. 2012)- by 2009, the phragmites stands had become less dense overall and were removed from some locations, but they estimated a few more years were still needed to eradicate the species from the area- that’s a long-term commitment and expense. And that same study that pointed out water hyacinth growth benefited from alligatorweed presence, also found that alligatorweed did better without water hyacinth- so if we clear out the water hyacinth, we could help increase the alligatorweed (‘tis a puzzlement).

So there’s a lot of work to be done with invasive plants, and plenty of room for each of us to help. For next week, I’m going to look into ways we can participate in invasive prevention, monitoring, and removal- we may not be able to turn back the clock on invasives, but we can try to limit their negative impacts.

Works cited:

Doyle, RD and RM Smart. 2001. Effects of drawdown and dessication on tubers of hydrilla, an exotic aquatic weed. Weed Science 49: 135-140.

He, Q, Cui, B, and Y An. 2012. Physical stress, not biotic interactions, preclude an invasive grass from establishing in forb-dominated salt marshes. PLoS ONE 7: e33164.

Hellmann, JJ, Byers, JE, Bierwagen, BG, and JS Dukes. 2008. Five potential consequences of climate change for invasive species. Conservation Biology 22: 534-543.

Lombard, KB, Tomassi, D, and J Ebersole. 2012. Long-term management of an invasive plant: lessons from seven years of Phragmites australis control. Northeast Naturalist 19 (Special Issue 6): 181-193.

Murray, JV, Stokes, KE, and RD van Klinken. 2012. Predicting the potential distribution of a riparian invasive plant: the effects of changing climate, flood regimes, and land-use patterns. Global Change Biology 18: 1738-1753.

Occhipinti-Ambrogi, A. 2007. Global change and marine communities: alien species and climate change. Marine Pollution Bulletin 55: 342-352.

Rogalski, MA and DK Skelly. 2012. Positive effects of nonnative invasive Phragmites australis on larval bullfrogs. PLoS ONE 7: e44420.

Rahel, FJ and JD Olden. 2008. Assessing the effects of climate change on aquatic invasive species. Conservation Biology 22: 521-533.

Wundrow, EJ, Carrillo, J, Gabler, CA, Hom, KC, and E Seimann. 2012. Facilitation and competition among invasive plants: a field experiment with alligatorweed and water hyacinth. PLoS ONE 7: e48444.